Process of preparing paving mixtures



Patented Aug. 27, 1935 UNITED STATES PATENT OFFICE PROCESS OF PREPARING PAVIN I MIXTURES Charles F. Carroll, Los Angeles, Calif., assignor to American Bitumuls Company, San Francisco, Calif., a corporation oi Delaware No Drawing. Application July 14, 1931, Serial No. 550,755

9 Claims. (Cl. 106-31) The invention relates to a method of coating dispersion of a bituminous substance with water, aggregates with bituminous materials in the manwhich may be a dispersion of a normally liquid ufacture of paving mixture and the like in which or semi-liquid bituminous binder in water, or a discrete particles of aggregates and. fillers are dispersion of a semi-solid or solid bituminous provided with substantially uniform and closely substance in water, such as are commonly known adherent films of bituminous binders whereby as asphaltic emulsions, and used in customary they may be laid or formed into coherent and highway construction. solid masses. The bituminous emulsion may be quick break- The invention is particularly adapted to roading of the type prepared by mixing molten or 10 way construction and affords a method of proliquid bitumen with alkaline water in the absence 10 ducing a composition of paving aggregates coatof material amounts of soaps, clays or other ed with bituminous materials capable of being emulsifiers, or it may be of the slow breaking laid hot or cold immediately after mixing, or type containing substantial proportions of soap, stored for considerable periods of time or transclay or the like. These emulsions or dispersions ported for substantial distances without deterioare considered of the oil-in-water type but emul- 15 ration. sions in which the phase is reversed and the wa- The invention contemplates the use of bituter dispersed throughout the bitumen are also minous emulsions to supply in part the binding embraced. effect for the aggregates and to supplement the The term bitumen is intended to cover pitches, binding efiect of bitumen in unemulsified form, asphalts and the like generally solid at atmos- 20 producing therewith a composite bituminous film pheric temperatures and capable of liquefaction on the surfaces of the said aggregates of desirable by heat. These materials are commonly referred characteristics as hereinafter pointed out. to as bituminous binders, paving asphalts and An object of the invention is to provide a coatbituminous or asphaltic cements. ed aggregate capable of being stored for substan- The term aggregates is meant to embrace a 25 tial periods of time or transported for considervariety of materials such as gravel or crushed able distances without deterioration and which rock, crushed brick, slag and the like, sand, may be bound together to form a compact mass pumice, burned clay, powdered limestone or other when desired, by merely subjecting the coated fillers, coal particles or other carbonaceous maaggregate to compaction or pressure. terial, granular or fibrous material or various 30 Another object is to present a method of applycombinations of these such as are generally suiting closely adherent bituminous films to aggreable for manufacture into unitary structures with gates wherein bituminous emulsions are emthe aid of suitable binders ployed. In carrying out the process, aggregates of suit- Another object is to disclose a method of able grading and character may be placed in a 35 coating aggregates with closely adherent bitusuitable mixer or pug mill and a quantity of minous films whereby the individual coated parbituminous emulsion added and thoroughly inticles are rendered temporarily non-adhesive. termixed therewith. The emulsion is preferably An t r j t s t d v s a m th d of app yof the quick breaking type comprising substans b tu us emulsions and molten bitumen tially equal proportions of asphalt and alkaline t0 aggregates whereby the coated Particles may water and free from kerosene, naphtha or other be handled in cold condition and compacted when volatile solvents of asphalt desired into l cohelient When thoroughly intermixed, generally after Another P P 15 to dlsclose various modlfica" less than one minute of agitation, hot molten twns. bltummous m formed Separate bitumen may be added and the mixing continued 45 applications of molten bitumen and bitummous until the bitumen is thoroughly and uniformly emulsion to aggregates. or Grated in the m ass Other objects and advantages of the invention 6 p th b d will be apparent from the following description The f aggrega' may en 8 and examples from the mixer and transported to the deslred 10- 50 The invention broadly Comprehend t addication, spread and compacted, or it may be stored tion of bituminous emulsion and molten bitumen in Stock P1165 9 subsequent The work to aggregates in separate steps and in either ability of the mlxtul'e y be controlled y the sequence. character of the bitumen in the bituminous emul- By the term bituminous emulsion is meant a sion, the softer the bitumen used, the longer the 56 mass will remain incoherent and non-adhesive before placing.

Increased workability may be attained by (11- luting the bituminous emulsion with water or adding water to the mass as a final step before removing the coated aggregate from the mixer.

The aggregates are preferably heated before placing in the mixer and this heating may be accomplished by the ordinary drying and heating equipment available in paving work, or the heating of the aggregate may be accomplished in whole or in part by mixing with sulphur or other combustible material which is ignited and completely consumed on the surfaces of the aggregate before the bituminous emulsion is added.

The heating and drying of the aggregate previous to its admixture with bituminous emulsion serves a valuable purpose in preventing the formation of moisture films between the aggregate and the bitumen deposited from the emulsion and thus insures a proper bonding and avoidance of any tendency toward peeling off, which might otherwise be encountered.

At any stage during the application of the composite film of bitumen as described the coating may be modified by the addition of powdered bitumen or the like to lower the penetration of the bitumen deposited and as a final step, dust or finely divided mineral matter may be added to the mix to prevent premature adherence of the individual coated particles, or solvents may be employed to soften the final coating if desired.

The invention is not limited to the application of bituminous emulsion and molten bitumen re spectively, in the sequence described but equally effective results are attainable if heated aggregates are first mixed with molten bitumen and bituminous emulsion added as a second step.

The following examples of the process of the invention as applied to the manufacture of paving compositions, will serve to indicate how the process may be properly carried out.

Example I .A quantity of crushed rock or gravel, sand and crusher dust proportioned as to particle sizes according to the well known practice of grading pavement aggregate mixtures and heated to a temperature between 200 and 300 degrees Fahrenheit is placed in a pug mill or mixer equipped with mechanically operated-paddles carried on revolving shafts.

Bituminous emulsion consisting of asphalt emulsified in alkaline water is added to the heated aggregate in the mixer in the proportion of approximately 2 to 4 percent by weight of the aggregate depending on the grading employed and the thickness of the composite coating required, and thoroughly mixed therewith.

Asphaltic cement, consisting of the residue from the distillation of petroleum which has been previously heated to a temperature of 2'75 to 350 degrees Fahrenheit, is then added to the mix in proportions of approximately 3 to 6 percent by weight of the aggregate, the amount of asphaltic cement being preferably in the ratio of 3 parts to 2 parts of bituminous emulsion. Mixing is continued until the asphaltic cement is thoroughly and uniformly incorporated into the mix.

The coated aggregate is then discharged from the mixer, transported to the desired location, laid in place, raked smooth and compacted by suitable means to a hard surface, or it may be stored in stock piles for future use without premature sticking or agglomeration such as would impair its workability. When the material is to unite to form a mass or body.

be stored for extended periods prior to use, particularly in cold weather, it may be desirable to increase the proportion of bituminous emulsion, in which event equal quantities of bituminous emulsion and asphaltic cement have been found suitable.

Example II .Mineral aggregate graded according to the pavement requirements is heated by any suitable means to a temperature between 200 and 300 degrees Fahrenheit and discharged into a mixer provided with suitable paddles or stirring devices.

Asphaltic cement as previously described, heated to a temperature of 275 to 350 degrees Fahrenheit is added to the aggregate in the mixer in quantity which, together with the bituminous emulsion to be subsequently added, will provide a mix of desired bitumen content.

Bituminous emulsion consisting of a semi-fluid petroleum residuum emulsified in approximately equal amount of water is then introduced into the heated mass in quantity from two-thirds to equal amount of the asphaltic cement previously added, and thoroughly intermixed.

The coated aggregate may be used for pavement construction at any convenient time thereafter by merely spreading and leveling to a uniformsurface and compacting by means of rollers or other suitable devices.

In either of the above examples the workability of the coated aggregates may be increased by additional water over that contained in the bituminous emulsion. In such event the water may be supplied by diluting the emulsion with 25 to '75 percent by weight of water, the emulsion being inherently capable of such dilution or being stabilized against breakdown due to such dilution. The additional water may also be added as a final step in the mixing process.

When bituminous emulsion is added to hot dry aggregates there is a tendency toward breakdown or separation of the constituents into free water and bitumen. The moisture is repelled from the heated surfaces of the aggregates and driven outward from the surface of the deposited bitumen film as steam or accumulated thereon or therein in the form of globules of free water. When hot asphaltic cement is subsequently added, the outward passage of moisture continues so that any free water remaining is accumulated in or on the outer surfaces of the composite film.

When hot asphalt cement is added to heated and dried aggregates there is notendency for moisture from the subsequent addition of bituminous emulsion to interfere with the bonding effect. It has been found that while a portion of the water content of the emulsion is converted into steam and driven off by the heat employed, a substantial portion of the water of emulsification remains as a complete or partial film of free water on the surfaces of the coated particles. This moisture coating tends to counteract the stickiness of the bituminous coating on the particles and to prevent the particles from adhering and forming a mass while the material is being manipulated or is in storage prior to use. The amount of water remaining on the surfaces of the coated particles may be controlled by suitably regulating the temperature of the aggregates and that of the asphalt cement. Lower temperatures leave more water and consequently more time or manipulation or storage before the particles adhere and Aside from the function of the water, in rendering the coated aggregates temporarily non-adhesive as above described, the same effect to a lesser degree may be accomplished by the substitution of viscous asphalts which are slightly fluid at atmospheric temperatures, for bituminous emulsions in the process of the invention.

Thus in Example II when a coating of asphaltic cement of usual low penetration customary in pavement practice is given an outer coating of an emulsion of semi-fluid petroleum residuum, the bitumen deposited from the emulsion would provide a semi-liquid protective film which would tend to prevent adhesion between the individual coated particles until such time as the two coatings become blended or fiuxed together. This feature is apart from and supplemental to the effect of the water from the emulsion and it is obvious that the semi-liquid petroleum residuum or flux could be employed in unemulsified condition and still aiford a degree of temporary nonadhesion and the same blending or fluxing effect.

While specific examples of certain methods for carrying out the invention have been given, it is understood that the invention is not limited thereby, but is intended to embrace all changes and modifications as come within the scope of the following appended claims.

ll claim as my invention:

1. The process of preparing paving mixtures of mineral aggregates coated with bituminous binders which comprises heating and drying the aggregates and mixing bitumen from separate sources, in the form of hot molten bitumen solid at atmospheric temperatures and in the form of aqueous bituminous dispersion, respectively, with the hot dry aggregates.

2. The process of preparing paving mixtures of mineral aggregates coated with bitumen which comprises heating the aggregates, adding a major portion of the bitumen in the form of hot molten asphalt solid at atmospheric temperatures and then adding the remainder of the bitumen in the form of an aqueous bituminous emulsion to the heated mixture.

3. The process of coating aggregates with bituminous films which comprises heating the aggregates, applying a first coating of hot, molten bitumen solid at atmospheric temperatures, and applying a second coating of aqueous bituminous emulsion to the hot, coated aggregates, whereby a composite coating is provided of predetermined characteristics dependent on the respective characteristics of the bitumen in the first and second coating, and having a protective film of moisture thereon adapted to prevent adhesion of adjacent coated particles.

4. The process of preparing paving mixtures of mineral aggregates coated with bitumen, which comprises heating the aggregates to a temperature sufilcient to expel moisture therefrom, adding a portion of the bitumen to the dry heated aggregates in the form of aqueous bituminous emulsion and then adding the remainder of the bitumen in the form of hot molten bitumen.

5. The process of preparing paving mixtures of mineral aggregates coated with bitumen containing moisture adjacent the outer surfaces which comprises heating the aggregates by means of dry heat to a temperature sumcient to eliminate all moisture therefrom, admixing a portion of the bitumen in the form of an aqueous bituminous emulsion with the dry heated aggregates whereby bitumen from the said emulsion is deposited on the surfaces of said aggregates and moisture repelled therefrom, and then admixing the remainder of the bitumen in the form of hot molten bitumen.

6. The process of preparing paving mixtures suitable for cold laying of mineral aggregates .coated with asphaltic binders which comprises heating the aggregates to a temperature sufiicient to eliminate moisture therefrom and adding asphalt in separate steps, in the form of hot molten paving asphalt and in the form of an aqueous emulsion of semi-liquid asphalt respectively, with the hot dry aggregates.

'7. The process of preparing paving mixtures suitable for laying cold of mineral aggregates coated with asphalt which comprises heating the aggregates to a temperature sumcient to expel moisture therefrom, adding a major portion of asphalt in the form of hot molten paving asphalt and then adding the remainder of the asphalt in the form of an aqueous emulsion of a substantially softer asphalt to the heated mixture.

8. The process of preparing paving mixtures of mineral aggregates coated with bitumen which comprises heating the aggregates to a temperature suflicient to expel moisture therefrom by means of dry heat, adding a minor portion of the bitumen to the dry heated aggregates in the form of aqueous bituminous emulsion, and then adding the remainder of the bitumen in the form of hot molten paving asphalt.

9. The process of preparing paving mixtures of mineral aggregates coated with bitumen containing moisture adjacent the outer surfaces which comprises heating the aggregates to a temperature sufficient to expel moisture therefrom, admixing soft bitumen in the form of an aqueous bituminous emulsion with the dry heated aggregates whereby bitumen from the said emulsion is deposited on the surfaces of said aggregates and moisture repelled therefrom and then admixing the remainder of the bitumen in the form of hot molten paving asphalt with the said aggregates.

' CHARLES F. CARROLL. 

